Interstitial cystitis/painful bladder syndrome/bladder pain syndrome (IC/PBS/BPS; hereafter IC) is a vexing and heterogeneous lower urinary tract disorder, currently defined by the International Continence Society as: an unpleasant sensation (pain, pressure, discomfort) perceived to be related to the urinary bladder, associated with lower urinary tract symptoms of more than six weeks duration, in the absence of infection or other identifiable causes. Diagnostic criteria have also been set forth by the National Institute of Diabetes, Digestive, and Kidney Diseases (NIDDK) and the European Society for Study of Interstitial Cystitis (ESSIC). Criteria from each of these organizations differ slightly, which renders the projected incidence and prevalence numbers of IC variable. This diagnostic uncertainty is further confounded by the overlap of IC with other functional pain syndromes including fibromyalgia, irritable bowel syndrome, chronic prostatitis/chronic pelvic pain, and vuvlodynia (sometimes confused with pain of bladder etiology), which have been posited to have similar pathophysiology. A method to quickly categorize/diagnose IC patients in a clinically relevant way that also predicts response to treatment would be a real clinical asset in that the most appropriate, patient-specific, therapy could be initiated early on in the process. Having biomarkers that define a specific IC subtype(s) could greatly facilitate diagnosis and treatment. The use of molecular tools, like gene expression profiling in relevant tissues, provides a feasible and effective approach for the identification of these biomarkers. We hypothesize that patients with IC can be categorized into clinically relevant groups based on the correlation of symptoms and/or clinical findings to gene expression profiles from patient bladder biopsy tissue. We further hypothesize that these biomarkers may be predictive, prognostic, and/or diagnostic. We will test these hypotheses by correlating subgroups of IC patients, designated based initially on bladder capacity, with gene expression profiles of those subgroups (Specific Aim 1). We will also correlate bladder tissue gene expression profiles with peripheral blood gene expression within the same IC patients to determine whether the peripheral blood harbors a clinically useful biomarker for IC sub-grouping (Specific Aim 2).